HP67 Voltages on Card Reader IC 1826-0322 (card reader sense amplifier)

[TI59]

Hello,

Findling around some hours trying to get HP67 card reader to work I got the feeling that the IC 1826-0322 (card reader sense amplifier) is faulty.

Since there is a potentiometer on the PCB I tried various settings - no remedy.

Using Multimeter with GB (Battery Pack -ve) I got against

Vm = 1,92 VDC
Vbb = 3,70 VDC
Vss = 6,15 VDC
Vbsw = 3,70 VDC = Mi
MTRS = 6,04 VDC

I disconnected Motor from PCB and put 3,70 VDC (battery pack) on it - gives a sound of speed wich I would state as normal - while putting card into reader with connected motor to IC with the 1,92 VDC on Vm the motor / card is crawling (2 mm / second)

Since the 1826-0322 is used in HP41 82104A card reader too - but with complete other schematics /logics a workaround would be purchasing such a card reader and use it as spare parts donator.

Any clue ?

Thanks for Help in advance,
Frank


Card reader
-----------


The 20 pin IC on the card reader PCB is the sense amplifier, write driver
and motor controller. The pinout is :


1826-0322


-----------
Vm --| U |-- Vbb
TR --| |-- Vss
GB --| |-- Vbsw
HAC --| |-- MTRS/
HA --| |-- MI (connected to Vbsw)
CA --| |-- WA
Gnd --| |-- RA
HBC --| |-- WB
HB --| |-- RB
CB --| |-- WE
-----------


Vm = Motor voltage output
TR = Motor speed control resistor (other end to Vm)
GB = Motor ground (to -ve side of battery pack and motor)
Vbb = Unswitched battery voltage
Vbsw = Switched battery voltage
Vss = +6.25V power input
MTRS/ = Motor run input
WA, WB = Write data inputs
RA, RB = Read data outputs
WE = Write Enable input
HA, HB = one side of head winding (for each track)
CA, CB = +ve end of 22uF cap (other side to HAC, HBC)
HAC, HBC = -ve side of 22uF cap, other end of head winding.

[teenix]

The voltages seem ok. The motor only runs at about 2.4V

Did the motor change speed when using the trimpot? If not, there may be a fault with the sense chip. Otherwise if the motor is running at speed and the card is still slow moving, check that the coupler that connects the spiral worm gear to the motor shaft has not perished like the drive wheel. If so, the motor will slip and not turn the gear properly.

cheers

Tony

[TI59]

(01-04-2024 11:56 PM)teenix Wrote:  The voltages seem ok. The motor only runs at about 2.4V

Did the motor change speed when using the trimpot? If not, there may be a fault with the sense chip. Otherwise if the motor is running at speed and the card is still slow moving, check that the coupler that connects the spiral worm gear to the motor shaft has not perished like the drive wheel. If so, the motor will slip and not turn the gear properly.

cheers

Tony

Hello Tony,

Thanks for the quick reply - I have managed to fix the issue by disassembling the whole motor/gear unit of the card reader. I assume the main show stopper was some really hardened gunk from the old rubber wheel plus a to long, pre-cut new silicon rubber tube I purchased from someone one eBay - this worked as sort of brake - cutting a tiny slice and lube the gear with special lube (polyurea (PU) grease - I can recommend this stuff - does not harden over time, does not harm plastic) the card reader now works perfect - even if the speed is definitely slower (-20%) compared to be driven with 2,4 VDC using my DC Power supply. The potentiometer is definitely working - operating from 0 - 10k linear. So I assume the 1826-0322 lost maybe the full amplification capability over the last 44 years - since I'm 55 years old I'm not as fast as I was with 18 years :-D

Kind regards,
Frank

[teenix]

Also make sure there is a tiny bit of backlash between the worm and drive gears. The worm shaft should move back and forth a tiny bit. If the shaft is sitting tight, it will stress the motor bearings.

Some molybdenum grease on the little ball bearing at the end of the worm gear helps it along too.

cheers

Tony